The instant invention relates to a hull construction for boats and the like and more particularly to a novel composite type hull construction.
Over the years steel hull constructions have proven to be extremely strong and durable and as a result virtually all of the very large vessels currently in use are made of steel. The most common type of hull construction for steel vessels incorporates a plurality of transverse steel ribs therein which are joined together with a plurality of longitudinal elements and stringers. This framework is covered with a shell of sheet steel to provide an outer hull for the vessel. Thereafter decking, interior compartments, bulkheads and superstructure are added to adapt the particular vessel for its intended service. Steel vessels of this general type derive their overall structural rigidity from the cooperation of the framework, the outer shell, the decking and the interior compartments and bulkheads. The structural relationships between these elements are well known and have heretofore been represented by mathamatical formulas which are widely used in naval architectural design. Unfortunately, however, while vessels constructed in this manner are very strong, they are also very heavy and the steel tends to rust and corrode rather quickly unless it is well coated and protected. For these and other reasons, the use of steel as a construction material for boat hulls has heretofore primarily been restricted to vessels of greater than 50 feet in length.
On the other hand, fiberglass hull constructions have in recent years proven to be extremely effective for smaller boats for both commercial and non-commercial applications. Fiberglass is a particularly desirable construction material because it is strong, durable, corrosion resistant and can be molded to virtually any shape. Traditional fiberglass hull constructions have generally included the laying-up of a number of layers of resin impregnated glass fibers into a preformed female mold. In this manner a laminate of a number of layers of glass fibers is formed to the precise configuration desired for the hull of the boat. Additional structural elements or stiffeners as well as decking and superstructure may thereafter be added to adapt each boat for its particular application. However, since in this type of construction the fiberglass shell or hull itself provides the primary structural rigidity for the vessel, as the size of the vessel or boat is increased, the number of layers or fiberglass necessary to obtain the desired structural rigidity must also be increased with the stiffeners, decking and bulkheads requiring similar reinforcing. While this is not of major concern in hull constructions for vessels of up to approximately 40 feet in length, it is of greater significance in boats in the range of between 50 and 70 feet resulting in disproportional increases in vessel weight. Furthermore, since boats of this general type are formed by laying up resin impregnated glass fibers into a female mold, as the size of the boat is increased, the associated problems related to the building, handling and moving of the mold as well as those related to the removal of the completed hull from the mold, become of greater significance. Consequently, while fiberglass boats of 100 feet or more in length have heretofore been made, for practical reasons, fiberglass hull constructions are really limited to boats of less than 65 feet in length.
The instant invention is directed to a novel hull construction which combines many of the advantages of fiberglass boats with those of steel boats. While the hull construction of the instant invention is adaptable for use on virtually any size vessel, it is particularly well suited for intermediate size boats in the range of between 40 and 120 feet in length.
The hull construction of the instant invention includes a rigid inner box-like structure which may be made of steel, aluminum or any other suitable rigid material. A rigid synthetic foam material is applied over the inner box-like structure and is formed to substantially the desired configuration of the hull. An outer layer of the resin impregnated glass fibers is layed-up over the foam material providing an outer skin or shell for the hull. In this manner a sandwich type composite hull is constructed which derives its structural rigidity primarily from the inner box-like structure and derives its outer configuration primarily from the foam material. The fiberglass shell merely provides a protective skin for the foam material.
Sandwich type hull constructions have heretofore been available wherein a synthetic foam material is sandwiched between inner and outer shells and examples of this type of hull construction representing the closest prior art of which the applicant is aware are illustrated in the following U.S. Pat. Nos.: Fisher, 3,013,922; Kohrn et al., 3,070,817; Hegg, 3,531,809; Geiger, 3,634,898; Bibb, 3,749,594; Moore et al., 3,831,212; Stoeberl, 3,811,141; Stoeberl, 3,840,926; Myers et al., 3,911,190; Alter et al., 4,021,874; Hoppe et al., 4,099,280; Holtom, 4,118,814; and Kostanecki, 4,161,796.
While there is obviously a considerable amount of prior art in the field of sandwich-type hull constructions, none of the hull constructions heretofore known have included the use of an inner box-like structure as the primary structural element of the hull. Thus, the instant invention is unique in that it combines the structural advantages of a steel hull construction with the practical advantages of a non-corrosive fiberglass outer hull in a sandwich type construction. The hull construction herein disclosed is both lighter and less expensive to manufacture than the hull constructions heretofore known. Consequently, the instant invention represents a substantial improvement in the art of sandwich-type hull construction and has significant commercial value as a result of substantial reductions in both hull construction costs and vessel operating costs.